1. Field of the Invention
The present invention relates to an image reading apparatus such as a scanner or copier, as well as to an image reading method and image forming apparatus, and more particularly, to an image reading apparatus that reads an original document placed on an original document platen and obtains the image data thereon, as well as to an image reading method and an image forming apparatus that use this image reading apparatus.
2. Description of the Prior Art
Scanners, copiers and similar apparatuses belonging to the conventional art use an image reading apparatus that reads an original document placed on an original document platen and obtains image data therefrom. Such an image reading apparatus may comprise an apparatus having a contact-type equal magnification optical system that is specially adapted to document reading or an apparatus having a reduction optical system that can also read some three-dimensional objects. A reading apparatus having a contact-type equal magnification optical system can be easily made compact in size, but because it has a short focal depth, is not well suited to reading three-dimensional objects. A reduction optical system-based reading apparatus, on the other hand, can read three-dimensional objects, but requires a long optical path from the original document to the photoelectric conversion element, and is accordingly more difficult to make compact in size than a contact-type apparatus.
The reduction optical system-based image reading apparatus 100 of the conventional art has an original document platen 101 on which an original document S is placed, as well as a first slider unit 102, a second slider unit 103, a lens 104 and a photoelectric conversion element 105 disposed underneath the original document platen 101, as shown in FIG. 10. Furthermore, the first slider unit 102 includes a light source 106, a reflecting plate 107 and a first reflecting mirror 108. The second slider unit 103 includes a second reflecting mirror 109 and a third reflecting mirror 110. In this image reading apparatus 100, the light emitted from the light source 106 irradiates the original document S either directly or via the reflecting plate 107. The light that reflects off of the surface of the original document S is reduced by the lens 104 and forms an image on the light-receiving surface of the photoelectric conversion element 105 via the first through third reflecting mirrors 108-110.
In connection with this type of image reading apparatus, a technology has been disclosed that employs an electroluminescent (EL) lamp as the light source 106, which traditionally comprises a fluorescent or halogen lamp (see, for example, Japanese Patent Application Laid-Open No. 2000-115470). This EL lamp can have a thin, flat construction and is used as a low-power, low-heat light source. The invention described in the cited patent document has, as a light source, an EL lamp having two longitudinal flat plate-shaped light emitting areas and a slit formed therebetween, enabling the height of the image reading apparatus (the vertical direction in FIG. 10) to be reduced.
However, in the conventional image reading apparatus 100 described above, the longitudinal EL lamp is moved by a slider unit. In this construction, in order to avoid contact between the original document platen and the slider unit, an appropriate distance must be maintained therebetween. In particular, where the user presses the original document onto the original document platen or a heavy original document such as a dictionary is placed on the platen, the platen may warp in the center. As a result, to allow for this warping, a gap of at least several millimeters must exist between the slider unit and the underside of the original document platen. At the same time, because a prescribed level of illumination must be received from the original document surface in order to obtain a certain level of output from the photoelectric conversion element, the greater the distance between the light source and the original document, the brighter the light source must be. Accordingly, an image reading apparatus that can be used with a lower-intensity light source is desired.
Although the conventional image reading apparatus 100 described above is more compact than in the case where the conventional fluorescent light source or the like is used, because a longitudinal flat plate-shaped EL lamp is mounted on a slider unit, it cannot be made sufficiently compact. Furthermore, in order to reduce the burden on the drive apparatus that drives the slider unit, it is preferred that the slider unit be made more lightweight and compact.